The present invention concerns imaging arrays and methods, particularly methods for correcting or compensating for defective or malfunctioning photodetectors in an imaging array.
Imaging arrays are electronic devices that sense light and output electrical signals representative of the sensed light. The imaging arrays are generally coupled to a television screen, computer monitor, or digital camera, which displays or records an image based on the output electrical signals.
An imaging array often includes a rectangular array or matrix of thousands or even millions of photodetectors, with each photodetector having a unique row and column position within the array which corresponds to a particular region, known as a pixel, of a displayed image. Each photodetector (or sensor pixel) converts sensed light into corresponding electric signals based on the intensity of the light. The electrical signals are converted into digital signals, comprising ones and zeros, which are processed by a digital-signal-processing circuit. This circuit ultimately outputs image signals to a device for recording or viewing.
One problem with conventional imaging arrays concerns defective or malfunctioning photodetectors. Defective photodetectors typically result in erroneous image signals that ultimately degrade the quality of resulting images. For example, an image based on imaging signals from an imaging array having a defective photodetector can have a black or dark area at the image region corresponding to the defective photodetector.
One limited solution to this problem has been to identify the defective photodetector and to generate a substitute image signal for the image signal of the defective photodetector, with the substitute image signal based on an average of the image signals from detectors surrounding it. See, for example, U.S. Pat. No. 5,854,655 (which is incorporated herein by reference). However, this solution suffers from the disadvantage that the substitute image signal introduces artifacts into the resulting image. The artifacts reflect the complete loss of information about the light actually striking the relatively large area corresponding to the defective photodetector.
Accordingly, there is a need for other methods of handling defective photodetectors.
To address this and other problems, the present inventor devised new imaging arrays and related methods for compensating for defective photodetectors. One exemplary embodiment of a new imaging array includes two or more group photodetectors, or xe2x80x9cgroup pixels,xe2x80x9d with each group pixel having two or more photodetectors coupled to produce a single group image signal. If the group image signal for a group pixel falls below some threshold level indicative of a defective or malfunctioning photodetector, the group image signal is amplified to compensate for the loss.
Various embodiments implement the photodetectors as passive or active photodiode circuits, as photogate circuits, as logarithmic sensor pixel circuits, or as charge-modulation devices. Some embodiments also implement the photodetectors as smaller-than-conventional photodetectors, that is, photodetectors having photo-sensing elements smaller than conventional elements.